The kerogen maturity (KM), also referred to as “Level of Organic Maturity” (LOM) of a geological area is related to its hydrocarbon potential, and can therefore be used in the assessment of the commercial value of a shale reservoir.
Several experimental techniques for estimating the KM of an area are available. Traditional techniques rely on the measurement of the temperature (Tmax) at which the maximum rate of hydrocarbon generation occurs in a kerogen sample during pyrolysis analysis, or the determination of vitrinite reflectance (% VR) by optical techniques.
More recent techniques are described in the scientific literature (“Structural evolution of organic matter during maturation of coals and its impact on petroleum potential and feedstock”, Org. Geochem. 62 (2013) 17-27; Characterization of organically Bound Oxygen Forms in Lignites. Peats and Pyrolyzed Peats by X-ray Photoelectron Spectroscopy (XPS) and Solid State 13C NMR Methods, Energy& Fuels 2002, 16, 1450-1462; “Three-Dimensional Structure of a Huadian Oil Shale Kerogen Model: An Experimental and Theoretical Study”, Energy & Fuels 2015, 29, 4122-4136). In these works, XPS is used to analyze kerogen structure, but no quantitative determination of KM is provided. In addition, experimental essays are carried out on an isolated carbon or kerogen sample, and not directly on a shale obtained from a reservoir.
As regards the patent literature, KM is the object of the following documents:
U.S. Pat. No. 8,906,690 B2: In this patent the KM of a formation sample is determined by using Fourier Transform Infrared Spectroscopy (FTIR).
US 2016/139293 A1: In this document, a method for determining a level of organic maturity of a shale gas formation is described. The method is based on inverting multifrequency complex conductivity data to estimate volume fractions of different organic components.
There are no patent documents in the literature related to the experimental determination of KM involving XPS measurements. In addition, the available techniques for experimental determination of KM are operator dependent, time consuming and require several sample preparation steps.
There is thus a need to provide a reliable experimental method which can be directly applied to a shale, in a more operator independent manner, in order to systematize the determination of kerogen maturity.